Process for the manufacture of unsaturated aldehydes from olefins



United States Patent O 7 Claims. (Cl. 260-604) ABSTRACT OF THEDISCLGSURE A process for the manufacture of unsaturated aldehydes fromolefins is provided wherein a mixture of the olefin and oxygen in amolar ratio oxygen to olefin within the range from about :1 to about0.5:1 is contacted in the vapor phase at a temperature within the rangefrom about 500 to about 1000 F. at which aldehyde formation proceedswith a catalyst composed of oxides of bismuth and molybdenum as theessential catalytic ingredients, promoted by a mixture of oxides ofbarium and silicon. The bismuth oxide is present in the catalyst in anamount to furnish a bismuth to molybdenum Bi:Mo atomic ratio of above1:3. The mixture of oxides of barium and silicon is present in thecatalyst in an amount of about 1 to about 5%, calculated as barium, andabout 1 to about 10%, calculated as silicon. If desired, the catalystcan also include phosphorus in an amount up to about 5% by weight.

This application is a division of Serial No. 395,978, filed August 19,1964, now Patent No. 3,280,166, dated October 18, 1966.

This invention relates to the catalytic oxidation of olefins tooxygenated hydrocarbons such as propylene to acrolein, using an improvedoxidation catalyst consisting essentially of oxides of the elementsbismuth and molybdenum, and optionally, phosphorus, promoted by oxidesof barium and silicon.

The Callahan, Foreman and Veatch US. Patent No. 2,941,007 describes theoxidation of an olefin such as propylene and the various butenes withoxygen and a solid catalyst composed of the Oxides of bismuth,molybdenum and silicon, and optionally, phosphorus. This cata lystselectively converts propylene to acrolein, isobutylene to methacrolein,aand B-butylene to methyl vinyl ketone and to butadiene, etc. Highyields are obtainable, although in the case of the butenes, carefulcontrol of reaction conditions may be required in order to direct thereaction in favor of either methyl vinyl ketone or butadiene, dependingupon which of these alternative products is desired.

The Idol, Jr., Patent No. 2,904,580, employs the same catalyst toconvert propylene, ammonia and oxygen to acrylonitrile, at approximatelyatmospheric pressures and elevated temperatures. Excellent conversions,usually in the range of 40 to 80%, nitrogen basis, of useful productsare obtainable.

I. THE CATALYST In accordance with the instant invention, the catalyticactivity of such bismuth oxide-molybdenum oxide catalysts is greatlyenhanced or promoted by the combination therewith of a mixture of bariumand silicon in the form of their oxides, referred to hereinafter aspromoters. The promoters in accordance with the invention are best3,362,998 Patented Jan. 9, 1968 applied by impregnation or surfacecoating of the catalyst, after its formation in accordance with theprocedure described in Serial No. 851,919, the disclosure of which ishereby incorporated by reference. Further, in accordance with theinvention, it has been determined that phosphorus oxide can also bepresent as a supplemental oxide.

The proportions of barium oxide and silicon oxide, with of withoutphosphorus oxide and/ or manganese oxide, are important in obtaining theoptimum enhanced activity. The barium oxide concentration, calculated asbarium, should be within the range from about 1 to about 5% by weight;and the amount of silicon oxide, calculated as silicon, should be withinthe range from about 1 to about 10% by weight, although more than 10%can be used, if desired.

While the catalyst of this invention may be employed without anysupport, it is desirable to combine it with a support. A preferredsupport is silica because the silica improves the catalytic activity ofthe catalyst. The silica may be present in any amount but it ispreferred that the catalyst contain between about 25 to 75% by weight ofsilica. Many other materials such as Alundurn, silicon carbide,alumina-silica, alumina, titania and other chemically inert materialsmay be employed as a support which will withstand the conditions of theprocess.

The catalyst may comprise phosphorus, also present in the form of theoxide. Phosphorus will affect, to some extent, the catalytic propertiesof the composition, but the presence or absence of phosphorus has noappreciable effect on the physical properties of the catalyst. Thus, thecomposition can include from 0%, and preferably from at least 0.1%, upto about 5% by weight of phosphorus oxide, calculated as phosphorus.

The promotor is incorporated with the catalyst base by impregnationthereof, using an aqueous solution, dispersion, or suspension of abarium compound and of a silicon compound, either the oxide, or acompound thermally decomposable in situ to the corresponding bariumoxide or silicon oxide, respectively, without formation of otherdeleterious metal oxide residue, for instance, barium acetate,fluosilicic acid, barium bromide, barium chloride, barium nitrate,barium peroxide, barium persulfate, barium propionate, ammoniumsilicofluoride, sodium silicate, potassium silicate, hydrous bariumsilicate, silicic acids, such as monosilicic acid and polysilicic acidsof low molecular weght, hydrous silica and colloidal silica. Afterimpregnation with such solution, employed in a concentration and amountto provide the desired amount of barium and silicon, the catalyst baseis dried, and then calcined at a temperature above that at which thecompounds applied are decomposed to the oxides. Temperatures in excessof 800 F. but below that at which the catalyst is deleteriouslyaffected, usually not in excess of about 1050 F., can be used.

The basic catalyst, composition comprises bismuth oride and molybdenumoxide, the bismuth-to-molybdenumratio BizMo being controlled so that itis at all times above 1:3. There is no critical upper limit on theamount of bismuth, but in view of the relatively high cost of bismuthand the lack of an improved catalytic elfect when large amounts areused, generally the atomic ratio bismuth to molybdenum BizMo of about3:1 is not exceeded. The nature of the chemical compoundswhich composethe basic catalyst is not known. The catalyst may be a mere mixture ofbismuth and molybdenum oxides, with or without phosphorus oxide, but itseems more likely that the catalyst is a homogeneous micro mixture ofloose chemical combinations of oxides of bismuth and molybdenum, with,optionally, phosphorus, and it is these combinations which appear toimpart the desirable catalytic properties construed as meaning that thecatalyst is composed of these compounds.

The barium and silicon compounds added thereto as promoters may or maynot enter into the chemical composition of the catalyst. Silicon addedlater with barium produces a difierent result from silicon added to acatalyst composition as a support and has a different function, sincethe enhanced catalytic effect is not obtained when silicon oxide iscombined as a support. Hence, the promoted catalytic effect may be dueto some complex silicon oxide-barium oxide combination formed on thesurface of the catalyst. In any event, the silicon and barium arepresent in the form of their oxides, when combined therewith later inaccordance with the invention.

The bismuth molybdate catalyst composition of the invention may have thefollowing composition ranges, as long as the atomic ratio of bismuth tomolybednum is above 1:3.

Element: Weight percent Bismuth 29.84-78.08 Molybdenum 11.32-47.29Oxygen 9.96-26.84 Phosphorus -2.40

This same composition may be expressed in the form of the followingempirical formula:

Bi P Mo O where a is 4 to 36, b is O to 2, and c is /2n-a+ /2m'b+ /2p-12a b 12 c'( 2)1 to 600 where a, b and c are as defined above.

When the silica is present as about 30 to 70 weight percent of the finalcomposition, the empirical formula is a b IZ c z) so to 150 where a, band c are as defined above.

To this are to be added barium oxide and silicon oxides, as such or asformed in situ from other added barium and silicon compounds, so thatthe empirical formula of the promoted catalyst in accordance with theinvention corresponds to the following:

4 72.s-97% (Bi P Mo O (stopwa- 1-6% BaO'2-21.5% sio The values of a, band c are in accordance with the definitions given above.

When the atomic ratio of bismuth to molybdenum BizMo is about 3:4, theempirical formula is The values of b and c are as defined above.

When the silica is present as about 30 to 70 weight percent of the finalcomposition, the empirical formula is r (6) 72.5 97% (Bi P Mo O (Si 2)3o150)' l-6% BaO-2-21.5% SiO where a, b and c are as defined above.

4 II. OXIDATION OF GLEFINS TO ALDEHYDES AND KETONES The reactants Thereactants used in the oxidation to oxygenated compounds are an olefin ormixture thereof and oxygen.

By the term olefin as used herein and in the appended claims is meantthe open-chain as well as cyclic olefins. Among the many olefiniccompounds which may be utilized in accordance with the process of theinvention, the following compounds are illustrative: propylene,butene-l, butene-Z, isobutylene, pentene-l, pentene-Z, 3-methylbutene-l,2-methyl-butene-2, hexene-l, hexene-Z, 4-methylpentene-l,3,3-dimethyl-butene-l, 4-methyl-pentene-2,

octene-l, cyclopentene, cyclohexene, 3-methyl-cyclohex one, etc. Thisinvention is directed particularly to the oxidation of the lower alkenes(3 to 8 carbon atoms) but higher alkenes may also be utilized witheflicacy. These compounds and their various homologs and analogs may besubstituted in the nucleus and/ or in the substituents in variousdegrees by straight-chain alicyclic or heterocyclic radicals. Theprocess of the invention is applicable to individual olefins as well asto mixtures of olefins and also to mixtures of olefins with thecorresponding or other saturated organic compounds.

The process of this invention is particularly adapted to the conversionof propylene to acroiein, isobutylene to methacrolein, alphaorbeta-butylene to methyl vinyl ketone, pentene-l or pentene-2 to ethylvinyl ketone and/ or pentene-3-one-2, 2-methyl-butene-2 to methylisopropenyl ketone, cyclopentene to cyclopentenone-2, and the like.

Straight-chain alpha-olefins of three or more carbon atoms, whenoxidized according to the process of the invention, tend to yield thesame products as the corresponding beta-olefins. Thus, as stated above,the alphabutylene, as well as beta-butylene, yields methyl vinyl ketone;and pentene-l, like pentene-Z, yields ethyl vinyl ketone. It is believedthat this results from isomerization of the alpha-olefins to thebeta-olefins under the reaction conditions.

It is surprising that the vinyl type carbonylic products obtained by theprocess of this invention are not always those which would be expectedfrom the direct substitition of an oxygen atom for two hydrogen atoms inthe allyl position, i.e., for two hydrogen atoms attached to a. carbonatom separated from the double bond by an intervening carbon atom. Forin the latter case beta butylene would form crotonaldehyde and notmethyl vinyl ketone. Instead, the reaction appears to be initiated atthe double bond and proceeds with the elimination of a hydrogen atom inthe allyl position and a change in position of the double bond.

The olefins may be in admixture with other hydrocarbons, for example, apropylene-propane mixture may constitute the feed. It is an advantage ofour process that the propane is not readily oxidized and passes throughthe reaction largely as an inert diluent. This makes it possible to useordinary refinery streams without special preparation. 1

Process conditions The temperature at which this oxidation is conductedmay vary considerably depending upon the catalyst, the particular olefinbeing oxidized and the correlated conditions of the rate of throughputor contact time and the ratio of olefin to oxygen. In general, whenoperating at pressures near atmospheric, i.e., 10 to p.s.i.g.,temperatures in the range of 500 to 1000 F. may be advantageouslyemployed. However, the process may be conducted at other pressures, andin the case where super atmospheric pressures, e.g., above 100 p.s.i.g.,are employed somewhat lower temperatures are feasible. In the case wherethis process is employed to convert propylene to acrolein, a temperaturerange of 750 to 850 F. has been found to be optimum at atmosphericpressure.

The apparent contact time employed in the process is not critical and itmay be selected from a broad operable range which may vary from 0.1 to50 seconds. The apparent contact time may be defined as the length oftime in seconds which the unit volume of gas measured under theconditions of reaction is in contact'with the apparent unit volume ofthe catalyst. It may be calculated for example from the apparent volumeof the catalyst bed, the average temperature and pressure of thereactor, and the flow rates of the several components of the reactionmixture. The optimum contact time will, of course, vary depending uponthe olefin being treated, but in the case of propylene the preferredapparent contact time is 1 to 15 seconds.

A molar ratio of oxygen to olefin between about 5:1 to 0.5 :1 generallygives the most satisfactory results. For the conversion of propylene toacrolein, a preferred ratio of oxygen to olefin is about 1:1. The oxygenused in the process may be derived from any source: however, air appearsto be the least expensive source of oxygen and it is preferred for thatreason.

We have also discovered that the addition of water to the reactionmixture has a marked beneficial influence on the course of the reactionin that it improves the conversion and the yield of the desired product.The manner in which water affects the reaction is not fully understoodbut the theory of this phenomenon is not deemed important in view of theexperimental results we have obtained. Accordingly, We prefer to includewater in the reaction mixture. Generally, a ratio of olefin to water inthe reaction mixture of 1:1 to 1:10 will give very satisfactory resultsand a ratio of 1:3 to 1:5 has been found to be optimum when convertingpropylene to acrolein. The water, of course, will be in the vapor phaseduring the reaction,

Inert diluents such as nitrogen, carbon dioxide, and saturatedhydrocarbons such as ethane, propane, and butane and pentane may bepresent in the reaction mixture.

In general, any apparatus of the type suitable for carrying outoxidation reactions in the vapor phase may be employed for the executionof the process. It may be operated continuously or intermittently andmay be a fixed bed with a pelleted catalyst or a so-called fluidized bedof catalyst. A fluidized catalyst bed simplifies problems of temperaturecontrol since coils through which water or other heat transfer medium iscirculated may be conveniently disposed in the bed to control thetemperature.

As stated above, pressures other than atmospheric may be employed inthis process but it is generally preferred to operate at or nearatmospheric pressure since the reaction proceeds well at such pressuresand the use of expensive high pressure equipment is avoided.

The reactor may be brought to the reaction temperature before or afterthe introduction of the vapors to be reacted. In large scale operation,it is preferred to carry out the process in a continuous manner and inthis system the recirculation of unreacted olefin and/or oxygen iscontemplated. Periodic regeneration or reactivation of the catalyst isalso contemplated. This may be accomplished, for example, by contactingthe catalyst with air at an elevated temperature.

The unsaturated carbonyl product or products may be isolated from thegases leaving the reaction zone by any appropriate means, the exactprocedure in any given case being determined by the nature and quantityof the reaction products. For example, the excess gas may be scrubbedwith cold water or an appropriate solvent to remove the carbonylproduct. In the case where the products are recovered in this manner,the ultimate recovery from the solvent may be by any suitable means suchas distillation. The efliciency of the scrubbing operation may beimproved when water is employed as the scrubbing agent by adding asuitable wetting agent to the Water, If desired, the scrubbing of thereaction gases may be preceded by a cold water quench of the gases whichof itself will serve to separate a significant amount of the carbonylproducts. Where molecular oxygen is employed as the oxidizing agent inthis process, the resulting product mixture remaining after the removalof the carbonyl product may be treated to remove carbon dioxide with theremainder of the mixture comprising any unreacted olefin and oxygenbeing recycled through the reactor. In the case where air is employed asthe oxidizing agent in lieu of molecular oxygen, the residual productafter separation of the carbonyl product may be scrubbed with anon-polar solvent e.g., a hydrocarbon fraction, in order to recoverunreacted olefin and in this case the remaining gases may be discarded.An inhibitor to prevent polymerization of the unsaturated products, asis well known in the art, may be added at any stage.

The following examples, in the opinion of the inventors, representpreferred embodiments of their invention:

Example I A bismuth silicophosphomolybdate catalyst base was prepared bythe following procedure:

74 g. of an phosphoric acid was added to 8330 g. of an aqueous silicasol containing 30% silica. Next, 2800 g. of bismuth nitrate wasdissolved in a solution made by diluting 160 ml. of 70% nitric acid to1540 ml. with distilled water. The bismuth nitrate solution was thenadded to the silica sol. Next, 1360 g. of ammonium molybdate wasdissolved in 1540 ml. of distilled water, and this solution added to thesilica sol. The resulting catalyst slurry was dried in an oven at 200 F.for 24 hours and then calcined in a furnace at 800 F. for 24 hours.After cooling, the catalyst was ground into particles, and screenedthrough a 10 mesh screen. A portion of the 8-10 mesh material was thenmade into tablets.

The final catalyst composition corresponded to the empirical formula BiPMo O (SiO having the following composition:

This tabletted catalyst was then impregnated with promoters inaccordance with the invention, by the following procedure:

25.9 g. of barium acetate was dissolved in hot water and diluted up to420 ml. This hot solution was used to impregnate 400 g. of the tablettedcatalyst prepared as described above, dipping tablets of the catalystcontained in a wire basket in the solution for 4 minutes, then removingand draining them for 4 minutes. By this procedure, ml. of the bariumacetate solution was absorbed by the catalyst, equivalent to 4.4 g. BaO.The wet catalyst was dried overnight.

The barium acetate-impregnated catalyst was impregnated a second time bythe above method using a solution prepared by diluting 206 g. of 30%fluosilicic acid solution to 420 cc. with water.

The impregnated catalyst was dried at 120 C. overnight.

The twice-impregnated catalyst of the invention then was calcined in airfor 12 hours at 800 F. Finally, the catalyst was ground and screened, toobtain a size fraction in the 8 to 10 mesh range.

Thus, the catalyst of the invention contained 1% added barium and 1%added silicon, together.

The barium and silicon promoted catalyst was employed in fixed bed formfor the conversion of propylene to acrolein. During the reaction thereactor was maintained at a temperature of 825 F. at atmosphericpressure. The contact time with the catalyst was approximately onesecond. The feed molar ratios were air/H O/ propylene/nitrogen, 6/ 1/32. Approximately 56% of the propylene feed was converted to acroleinand about 31% of the propylene was unreacted. This unreacted materialcould be recycled. The remainder of the product consisted of carbonoxides, minor amounts of low molecular weight carbonylic compounds, andorganic acids.

Example II The bismuth silicophosphornolybdate catalyst of Example I wasemployed to prepare another promoted catalyst corresponding to that ofExample I but with a greater amount of barium. The catalyst of theinvention contained 3% added barium and 1% added silicon, as the oxides.

The catalyst of the invention containing 3% added barium and 1% addedsilicon was used in the conversion of propylene to acrolein in a fixedbed. During the reaction, the reactor was maintained at a temperature of850 F. at 6 p.s.i.g. The apparent contact time with the catalyst wasapproximately 2.8 seconds. The feed molar ratios were propylene/air/HO/nitrogen, 1/ 11/ 2/ 12. Approximately 53% of the propylene feed wasconverted to acrolein. The total conversion was 79.7% of the propylenefeed, the remainder consisting of 0.5% acetaldehydc, 2.9% acrylic acid,1.3% acetic acid, and carbon oxides.

All percentages in the specification and claims are by weight, in thecase of the catalyst composition, and by volume in the case of gases.

We claim:

1. A process for the manufacture of unsaturated aldehydes from olefins,which comprises the step of contacting in the vapor phase at atemperature within the range from about 500 to about l-000 F. at whichaldehyde formation proceeds, a mixture of the olefin and oxygen in amolar ratio oxygen to olefin within the range from about 5:1 to about0.5 :1 with a catalyst consisting essentially of oxides of bismuth andmolybdenum as the essential catalytic ingredients, the bismuth oxidebeing present in an amount to furnish a bismuth to molybdenum BizMoatomic ratio of above 1:3, promoted by a mixture of oxides of barium andsilicon, in the proportion of about 1 to about 5%, calculated as barium,and about 1 to about 10%, calculated as silicon.

2. A process irr accordance with claim 1, in which the olefin ispropylene.

3. The process in accordance with claim 1, in which the catalyst alsoincludes phosphorus in an amount up to about 5% by Weight.

4. The process in accordance with claim 1, in which the catalyst has acomposition corresponding to the empirical chemical formula:

72.597% (Bi P Mo O )-16% BaO-22l.5% SiO where a is a number Within therange from about 4 to 36, b a number within the range from 0 to 2, and cis /2n-a+ /2m-b+ /2p-12, wherein n, m and p are the average valences ofbismuth, phosphorus and molybdenum, respectively, in the catalyst.

5. The process in accordance with claim 1, in which the catalyst issupported on silica.

6. The process for the manufacture of unsaturated aldehydes fromolefins, which comprises contacting in the vapor phase at a temperaturewithin the range from about 5-00 to about 1000 F., a mixture of anolefin having from three to eight carbon atoms, and oxygen in a molarratio oxygen to olefin between about 5:1 to 0.5 :1 with a catalystconsisting essentially of oxides of bismuth and molybdenum as theessential catalytic ingredients, the bismuth oxide being present in anamount to furnish a hismuth to molybdenum BizMo atomic ratio of above1:3, promoted by a mixture of oxides of barium and silicon, in theproportion of about 1 to about 5%, calculated as barium, and about 1 toabout 10%, calculated as silicon.

7. A process in accordance with claim 6, in which the olefin ispropylene.

No references cited.

LEON ZITVER, Primary Examiner.

R. H. LILES, Assistant Examiner.

